Radical polymerization of styrene is well-known in the art and is suitably accomplished by subjecting styrene monomer to elevated temperatures in the range of about 150.degree. and 250.degree. C; U.S. Pat. No. 3,859,268. Generally styrene addition polymers contain lower oligomers, for example, cyclic dimers and trimers, which impart undesirable physical properties to these products and may impart toxic properties to further functionalized polystyrene derivatives. They may contain residual unsaturation which also renders such products less useful for applications where the color of such products is detrimental and where further functionalized materials, e.g., chloromethylated and quaternary ammonium derivatives, are used since cross-linking may occur in the processing of such materials as a result of the residual unsaturations rendering the products unfit for the intended utilities. Generally, thermally polymerized polystyrene has a wide molecular weight distribution rendering it less suitable for certain applications which require sharp melting points.
Cationic polymerization of styrene monomer with a proton acid is one of the early polymerization reactions studied; U.S. Pat. No. 2,499,796. Cationic polymerization of styrene and other ethylenically unsaturated monomers has been widely studied on a lab scale, "The Chemistry of Cationic Polymerization" (P. H. Plesch, Editor, 1963) and has been used commercially for production of synthetic rubber from isobutylene alone or with comonomers such as styrene, etc. but at low temperatures generally of less than about 0.degree. C and preferably lower; U.S. Pat. Nos. 2,974,126 and 2,643,993. .alpha.-Methylstyrene has also been cationically polymerized but likewise at sub-zero temperatures; U.S. Pat. Nos. 3,669,947 and 2,941,989. t-Butylstyrene has been cationically polymerized at more convenient temperatures of about 25.degree. C to 125.degree. C but gives a very low molecular weight product of about 500-2500; U.K. Pat. No. 1,232,610.
Styrene alone has been cationically polymerized but at low temperatures on the order of -50.degree. C to -150.degree. C; U.S. Pat. No. 2,436,614. At ambient temperature the reaction has primarily been studied as a laboratory curiosity generally for kinetic and mechanistic purposes; see for example Chapter 6 of Plesch, previously cited. Perhaps the lack of commercial interest in the cationic polymerization of styrene is due to poor physical properties of products heretofore obtained from such processes as is evidenced by comments found in "Cationic Polymerization of Olefins: A Critical Inventory" Joseph P. Kennedy (Wiley-Interscience, 1975) at page 229 and at page 238 where he concludes that the process will probably remain unattractive for large-scale commercial exploitation in the future.